Halogenation of nitro compounds



Patented Dec. 28, 1943 HALOGENATION OF NITRO COMPOUNDS Earl 'r. McBee and Elizabeth F. RileyeWest Lafayette, Ind., assignors .to Purdue Research Foundation, La Fayette, Ind., a corporation of Indiana No Drawing. Application August 3, 1940,

Serial No. 351,142

1'] Claims.

Our invention relates to the chlorination of nitro compounds, and more specifically to the chlorination of organic compounds having a saturated group of at least 2 carbon atomswith a free nitro group attached thereto.

The chlorination of free nitro compounds, as opposed to salts of nitro compounds, is disclosed in our co-pending application, Serial No. 351,141. In accordance with the disclosure of this application, nitro compounds having a saturated group of at least 2 carbon atoms with a free nitro group attached thereto, are subjected to substitutive chlorination, to obtain chloronitro compounds in which the chlorine and nitro group are attached to different carbon atoms.

In this manner all of the various monochlorinated derivatives having the chlorine and nitro groups attached to different carbon atoms, may be prepared, and polychlorinated derivatives may also be produced, if desired. The preferred procedure constitutes liquid phase chlorination, utilizing substantially anhydrous reactants.

We have now found that the yields and conversions obtainable in the liquid phase chlorination process may be considerably improved ii, in addition to employing substantially anhydrous reactants, the reaction mixture is subjected to the action of a dehydrating agent during the chlorination reaction. Since no water is formed in the substitutive chlorination reaction, it is difficult to explain the improved results obtainable by the use of a dehydrating agent. It is possible .that small amounts of water are formed in some side reaction, with a resulting adverse effect on the chlorination reaction, but it is to be understood that our invention is not to be construed as limited to any particular theory of its operation.

The present process is applicable to the chlorination of any organic compound having a saturated group of at least 2 carbon atoms, such as an aliphatic or alicyclic group, with a free nitro group attached thereto. Our process is particularly suited for the chlorination of nitro hydrocarbons, and especially nitroalkanes of at least 2 carbon atoms. Chlorine is preferably employed as the chlorinating agent, but other-chlorinating agents which are suitable for the chlorination of aliphatic hydrocarbons, and which are not adversely affected by the presence of nitro groups, may also be used if desired.

The chlorination may be carried out in accordance with known practices for the liquid phase chlorination of aliphatic hydrocarbons, and our invention is especially suited for use inliquid phase photochemical chlorinations. The procedures for the various liquid phase chlorinations may follow in all respects the methods described in U. S. Serial No. 351,141. referred to above. Reaction times and temperatures, and the amount and kind of light employed, may be chosen in accordance with prior practices, and our invention is not limited to any particular procedure in this respect. Any of the various modifications of procedure, previously used in this art, may be followed, and our present invention differs from the prior art only in the use of a dehydrating agent.

Our chlorination process is particularly applicable tochlorination of various nitro hydrocarcons, and especially the nitroalkanes containing 2 or more carbon atoms. As examples of the nitro compounds which may be treated in accordance with our invention, there may be mentioned nitroethane, l-nitropropane, 2-nitropropane, 1 nitrobutane, 2-nitrobutane, 1-nitro-2-methylpropane, nitrocyclohexanes, phenylnitroethane, and the like.

Any dehydrating agent which is chemically inert to the reactants, and which has dehydrating action under the conditions of the reaction, may be employed. As examples of such agents, there may be mentioned phosphorus pentoxide, anhydrous calcium sulfate, anhydrous magnesium sulfate, and dehydrated silica gel. We prefer to employ phosphorus pentoxide in most cases.

The dehydrating agent may be maintained in the reaction mixture in the reaction zone during the entire reaction. Alternatively, the reaction mixture may be circulated successively through the reaction zone, then in contact with an insoluble dehydrating agent, and then recycled back to the reaction zone. Various other modifications or equivalent procedures will be apparent to those skilled in the art.

The amount of dehydrating agent to be employed will depend upon the particular agent chosen. and the procedure utilized. If the dehydrating agent is extremely inert, chemically, or is not maintained in the reaction mixture throughout the reaction, a large excess over that required will usually have no adverse effects.

However, in the case of more reactive dehydrating agents such as phosphorus pentoxide, it is usually desirable to employ the minimum amount which is effective in producing the maximum increase in yield and conversion. We prefer to employ phosphorus pentoxide in amounts ranging from 0.01% to 1.0% by weight, based on the weight of the nitro compound being chlorinated.

2 ass-1,01: lquivalentamoimts oi'otherdehydratingasenis Pr pane. The reaction mixturewls fractionalmay suitably be employed. 1y distilled to recover unreacted l-nitro Ou invention may be further illustrated by and chlorinated products. No l-nitro-l-chlorothe following speciilc examples: propane was found, but i-nitro-2-chloropropane m1 I wasohtainedinayield oi 38.2% oi'thetheoretical yield (26.6% conversion) based on l-nitro- Buhstun rine s b ed propane. 1-nitro-3-ch1oropropane was obtained in a yield oi 39.7% of the theoretical yield (27.7% conversion) based on l-nitropropane.

Substantially anhydrous chlorine was bubbled for 24.5 hours at 58-80 0., while exposing the is reaction mixture to lisht under conditions of tmeoi 50C. Attheconclusion mmplemnuringthisperiodchlorinereotthemactimthelnltturewasdistilledtoreactedtoflieextentoiapartsbyweightperlflil coves unreacted nitroethane, and l-chloro-2-niparts bywelght or nltrobutane. At the conclusionoithechlorinationthereactionmixturewas 2o iractionally distilled to recover um'eacted l-niphoaphoru pentoalde was incorpotrobuiane and chlorinated products. It was rated in the nitroethane, in a concentration oi round that approximately 87% oi the i-nitrobuimibyweishtandthatinthepresenceor tanehadreactedintheprocess,andthatnoihi phosphorus pentotlde, the temperature oi chloro-l-nitrohutane was produced. Threemom the reaction mixture was approximately 59' C. 26 ochlorinated l-nitrobutanes, boiling at 67' 0., 87' 'lmtead oi 50' C. The following yields and con- 0, and 101' 0, respectively, at 6.5 millimeters versionswereobtained: pressure, were obtained in yields or 11.8%,

27.3%, and 16.4% respectively, based on l-nitrom butane. mmmm Oonvusion, Yield, Exams v p m ml mums-1 i-nitropropane was vaporized and passed, to-

sether with gaseous chlorine, in a ratio of apas 0,, a0 1.2 proximately) parts byweight oi chlorine per M ss loom-is byweisht oi 1-nltropropane,throuha maintained at 300 0. lbs

Isa-run moi'ilowwassuchg'haianaveragecontact m u oiapproximately seoondswasobtained. mm of pug-2 o m 'lhereactionwaseiiectedintheahsenceotlisht. wasinadeintheahsenceoi gm sthereactionchamberwas mwmmw 035% m, condensed,andthecondensate subjectedtoi'ractional distillation to recover unreacted l-uitropropane and chlorinated products. Both i-nitro-2-chloropropane anti 1-nitro-3-chloropro- 48 pane were obtained, but no l-nitro-l-chloropropane was found to be present in the reaction nomthewalloi'theflask. Theamountoichlorinereacteddm'ingthisperlodwasiolmdtohe approximately 8 parts by weight per 100 parts so hyweisht oinitroethane. Thereactionmixture was then subjected to fractional distillation to recover unreacted nitroethane, and l-nitro-2- chloroethane. The yield of the latter product manilallyanhydrouschiorinewasbubbied wasmAvtoithetheoreflcalyieldba-sedonnimm anhydroml-nitropropanelltroethsne. fil'llhoursat 58C.,durins Mm whehtimethereactlonininturewasexposedina uinchdialneterslalstubethreeteetlmmto amctionmixmrecomprisingl-nltropropane Mitmmwattincandeseenttunssteniilaandliquidchlorinatosetherwithcarbontetm. amt lishbspacedammatelyiinchesh'om 1o chlorldeasasolventwaspumpedatapressure thatubewallat ofapprolimatelylo oilililopoundspersquueinemmmu lndiasim'wmthemthofthetuhe. At actionchambermaintainedat235C..atarate flieomchuionoitbechlorlnatiomitwas found sivlngacontacttimeoi'approximately 1.3 minfliatchlorinehadreactedtotheextentatlito uteaThereactionmixtui-econtainedappronparhwweishtollilirpartsbywdshtotnitro- 7lmately12partshyweishtoi'chlorine.and85il product. dime-mm I alumm v1 a e M. 50 Substantially anhydrous chlorine was bubbled mm 0 Con m comma, through substantially anhydrous nitioethane ior maul-nicom m... 1% s hours at to c. followed by 8 hours at to c. m During the chlorination the reaction mixture was csposedinaioomlrolmdbottomslassiiaskto no as: 55 lishtiromtwo'ailowatttlmsstenfllament incana m descent lishts placed approximately two inches Dinah.

parts by weight of carbon tetrachloride per 100 parts by weight of l-nitropropane. The reaction was eiIected in the absence of light. The pressure was released on the reaction mixture issuingirom the reaction chamber, allowing unreacted chlorine to escape, and the liquid reaction .product was subjected to 'iractional distillation to recover unreacted l-nitropropane and chlorinated products. No. l-nitro-l-chloropropane or l-nitro-2-chloropropane were found, but l-nitro- 3-ch1oropropane was obtained in an amount constituting 6.1% conversion based on 1-nitropro-.- pane, and 40.8% based on chlorine.

It is to be understood of course, that the above examples are merely illustrative, and donot limit the scope 01' our invention. As has previously been pointed out our invention is broadly applicable to the liquid phase photochemical chlorination of nitro compounds having a saturated group of at least two carbon atoms, with a free nitro group attached thereto, and is not limited to any particular nitro compounds, chlorinating agents, or chlorination procedure. In general it may be said that the use or any equivalents, or modifications of procedure, which occur to those skilled in the art, is included in the scope of our invention.

This is a continuation-in-part of our copending application U. S. Serial No. 351,141, filed Aust 3, 1940.

Our invention now we claim is:

1. .In a process for the production of organic chloronitro compounds, the step which consists substantially in contacting chlorine with an organic compound containing a saturated aliphatic group of at least 2 carbon atoms and having a free nitro group attached to one of said carbon atoms, under substantially anhydrous conditions, in the substantial absence of other compounds tending to react with said nitro compound and with chlorine, and for a time sufllcient to replace at least one of the hydrogen atoms of said hydrocarbon group with a, chlorine atom, whereby a chloronitro compound is obtained containing chlorine attached to a carbon atom other than the one to which the nitro group is attached, the reaction being effected in the presence of an initially added dehydrating agent that is inert with respect to the reactants.

2. The process of claim 1 wherein said nitro having been described, what organic compound is contacted with said chlorine while in the liquid stage.

3. The process of claim 1 wherein said nitro organic compound is a nitroalkane.

4. The process of claim 1 wherein said nitro organic compound is contacted with said chlorine under the action of light.

5. The process of claim 1 wherein said dehydrating agent is phosphorus pentoxide.

6. The process of claim 1 wherein said dehydrating agent is phosphorus pentoxide in amount ranging from about 0.1 to 1.0 percent based on the weight of the nitro organic compound.

l. The process of claim 1 wherein said nitro organic compound is a nitroalkane and said dehydrating agent is phosphorus pentoxide.

8. In a process for Z-nitroethane, the step which consists substantially of contacting substantially anhydrous chlorine with substantially anhydrous nitroethane in the liquid phase in the presence of light and phosphorus pentoxide but in the substantial the production of l-chloroabsence oi other compounds tending to react with .said nitroethane and with chlorine, and for a time sumcient to replace at least one of the hydrogen atoms of said nitroethane with chlorine, thereby forming said 1-chloro-2-nitroethane.

9. In the process for the production of chloronitropropanes having chlorine attached to a carbon atom other than the one to which the nitro group is attached, the step which consists substantially in contacting substantially anhydrous chlorine with substantially anhydrous nitropropane-in the liquid phase in the presence of light and phosphorus pentoxide but in the substantial absence of other compounds tending to react with said nitropropane and with chlorine, and for a time suillcient to replace at least one of the hydrogen atoms of said nitropropane with chlorine, thereby forming achloronitropropane in which the chlorine atom is attached to a carbon atom other than that to which the nitro group is attached a 10. In the process for the production of organic chloronitro compounds, the step which consists substantially in contacting chlorine with an organic compound containing a saturated aliphatic group of at least 2 carbon atoms and having a free nitro group attached to one of said carbon atoms, under substantially anhydrous conditions, in the substantial absence of other compounds tending to react with said nitro compound and with chlorine, and for a time sufllcient to replace at least one of the hydrogen atoms of said aliphatic group with a chlorine atom, whereby a chloronitro compound is obtained containing chlorine attached to an aliphatic carbon atom other than the one to which the nitro group is attached.

11. The process of claim 10 wherein said organic nitro compound is contacted with said chlorine under the action of light;

12. The process of claim 10 wherein said organic nitro compound is a liquid nitroalkane.

13. The process of claim 10 wherein said organic nitro compound is a nitroalkane in the vapor phase.

14. The process of claim 10 wherein said organic nitro compound is a. nitroalkane in the vapor phase and maintained under super-atmospheric pressure.

15. In aprocess for the production of l-chloro Z-nitroethane, the step which consists substantially in contacting substantially anhydrous, chlorine with substantially anhydrous nitroethane in the presence of light, in the substan-' tial absence of other compounds tending to react with said nitro compound and with chlorine and for a time suflicient to replace at least one of the hydrogen atoms .of said nitroethane with a chlorine atom, whereby a chloronitroethane is obtained containing chlorine attached to a carbon atom other than the one to which the nitro group is attached.

16. In a process for the production of chloronitropropanes, the step which consists substantially in contacting, in the liquid phase and in the presence of light, substantially anhydrous chlorine with substantially anhydrous nitropropane in the substantial absence of other com-. pounds tending to react with said nitropropane and with chlorine, and for a time suflicient to replace at least one of the hydrogen atoms of said nitropropane with a chlorine atom, whereby a chloronitropropane is obtained containing chlorine attached to a carbon atom other than the one to which the nitro group is attached. 

